Sifo Diyas = Plagueis? If the shoe fits...
We all know that a deceased Jedi Master named Sifo Diyas who was "killed" some time around the Episode I era had placed an order for the Clone Troopers on behalf of "The Republic."
A Sith masquerading as a Jedi is possible especially since we know they can hide themselves well.
If Plageuis had the power to create life and presumably created Anakin (speculation, I know), perhaps this was kept a secret until years later, when his apprentice, (Sidious) finds out and was threatened by this (I mean, he essentially created his replacement) so he kills Plageuis/Diyas in his sleep, and takes up an apprentice of his own (Maul) and carries on what may have originally been Plageuis' plan to take over the Republic.
Six months to a year later, the events of Episode I take place. Maul is dead, and Palpatine is surprised to find his old Master's creation was found and will be trained in the Jedi arts. (Plapatine clearly showed interest in Anakin very early on. Why would that be?) Perhaps he figures he could utilize this power for himself. So he befriends him, supports him, meanwhile biding his time and waits to set him down the path we all know he goes.